These are the words of Mumia Abu-Jamal, a revolutionary journalist and former Black Panther who was sentenced to death for the murder of Philadelphia police officer Daniel Faulkner in 1982.

Described by many as the “voice of the voiceless,” Mumia has remained an outspoken critic of the US political system from the darkness of his prison cell. Over the last 26 years he has written more than 500 columns, published five books and uses his weekly phone calls to record radio broadcasts for Prison Radio.

On Thursday night a documentary about his life and incarceration, In Prison My Whole Life, had its UK premiere. The bar of the Ritzy cinema in Brixton, usually home to a smattering of fashionistas, was buzzing with the clink of wine glasses, earnest conversation and Amnesty workers clutching petitions.

Inside the old theatre hall-turned-cinema, the red velvet chairs were draped with a campaigner’s goody-bag filled with political leaflets and peanuts.

The evening began with a series of readings from the who’s who of British acting talent. Lead by Colin Firth, whose wife Livia produced In Prison, Alan Rickman, Juliette Stevenson and Kelly MacDonald read extracts from A People’s History of the United States by Howard Zinn, accompanied by performances from Beverly Knight and Ben Barnes.

The film is narrated by William Francome, an American-raised Brit who was born on the day that Mumia was arrested. It opens with his words: “I have been aware of Mumia for as long as I can remember… I am going on a journey to find out about the man who has been in prison my whole life.”

Approaching the case 26 years on, Francome pulls apart the flaws of a trial which Amnesty International described as “in violation of minimum international standards”. What he finds is a catalogue of errors that have been ignored by the legal system, including a racist judge, omitted and tampered evidence and falsified testimonies.

Throughout, Francome himself serves as a concrete reminder of the length of time that Mumia has spent in jail. Yet as the film goes on, what starts as an analysis of a single case opens into a more general critique of racial equality in the US and the vast disparities that still exist today.

From the FBI assassination of Black Panther leaders in the 1970s to the heartrending pictures of the victims of Hurricane Katrina, Francome explores why Mumia has become such an emblematic figure for so many and how much further there is to go before justice becomes truly blind.

Backed by MySpace, In Prison emulates what its director, Marc Evans, described as the “digital documentary style,” a testimony to its humble beginnings as Francome’s personal project. It serves to show, Evans said at the film’s world premiere in Rome last year, that despite “so much media noise”, the “dissenting voice still exists today”.

In Prison My Whole Life is due to be released to DVD in the UK later this year and is showing in London cinemas until the 29th October.